ferrite coils

https://donovanxubs438.edublogs.org/2020/05/24/what-i-wish-i-knew-a-year-ago-about-ferrite-core-for-power-cord/

A ferrite core is usually a form of transformer that may be used in small transformers. It may be named a hollow core or semi-rigid Main. It features a Main or envelope with attached plates which happen to